In semiconductor epitaxial deposition process, if the difference of a lattice constant is too large between the material of epitaxial substrate and the deposition substrate, for example, gallium nitride (GaN) deposits on silicon (Si) substrate. It will exist a stress between the two materials, and form a curved surface on the substrate. This phenomenon will reduce the quality of the epitaxial of the process, and cause an increased cost in manufacturing. Therefore, in the epitaxial process, the change of the curvature of the substrate needs to be monitored in real time and then understand the stresses in the layers of the structure which is most obvious immediately. The research is important to adjust the corresponding parameters to reduce the stress for all of the manufacturers.